Embodiments of present technique relates to power converters and more specifically to a method of operating a three-level two-stage decoupled active neutral point clamped (NPC) converter.
Turboelectric or hybrid electric propulsion can increase aircraft energy conversion efficiency, reduce carbon emissions, and decrease dependency on carbon-based fuels. A megawatt (MW)-class light-weight high-efficiency high-reliability power converter is an essential component of hybrid electric propulsion. Further, to reduce the cable weight, the power converter needs to withstand medium direct current (DC) voltage stress. Moreover, to reduce the weight of a motor used in the hybrid electric propulsion, the power converter output fundamental frequency needs to be high, e.g. above 1 kHz, which accordingly requires higher switching frequency for the power converter.
Silicon carbide (SiC) is a semiconductor that is increasingly being used in power electronic devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) to meet the high switching frequency and efficiency requirements of power converters. Further, a three-level NPC converter topology is preferred for the power converter, since it can achieve higher voltage rating without devices serialization, better harmonic performance to reduce filter weight, and lower switching loss for high efficiency.
To design such a three-level converter, the foremost challenge is how to minimize a commutation loop inductance. Other than the commutation loop inductance, there are other challenges for SiC MOSFET based multilevel converter as compared to Si IGBT modules. The SiC MOSFETS modules are much more expensive than Si IGBT modules and have intrinsic thermal unbalance characteristics. Methods have been proposed to effectively mitigate the thermal unbalance issue. However, such methods shift more switching actions from a short commutation loop to a long commutation loop. Such methods will lead to much higher system level switching losses.
Therefore, a system and a method that will address the foregoing issues is desirable.